As the corruption case involving former Cabinet secretary-general Lin Yi-shih (林益世) continues to draw attention, the Supreme Prosecutors’ Office Special Investigation Division (SID) is dealing with Lin’s family and they have also started to conduct lie detector tests, or polygraphs, on those suspected of involvement in the case. However, caution needs to be taken with such tests and criminal prosecutions and investigations must avoid becoming overly reliant on them.
The efficacy of lie detector tests is based on several premises: The first is that the true or false nature of what a person is asked will arouse certain physiological reactions in the individual which can be registered by the lie detector if the person is unable to control them. It is also based on the premise that experts can then interpret these results. While these premises seem to be scientific, they have always been surrounded by much controversy and doubt.
There are many reasons why people question the efficacy of polygraphs. These include questions over their objectivity, especially when it comes to confirming the expertise of the person administering the test, whether the device used meets the required standards and whether the testing environment is controlled. These things all influence the outcome of a test.
Also, because each person’s physiology is unique, how can there be a uniform set of standards for judging test results? Other types of forensic testing, such as DNA tests, are not subject to these problems. This not only makes them highly accurate, the results can also be reviewed and verified by other experts using similar procedures.
However, because lie detector tests cannot eliminate many of the above-mentioned problems, they lack reproducibility, a trait heavily emphasized by modern science. It is therefore not possible to clarify how accurate the administration and outcome of a lie detector test was. These are issues that make such tests less reliable.
Criminal investigations in Taiwan may involve the use of polygraph exams with several conditions. One requires that test administrators have proper professional training and experience, another requires confirmation that the lie detector is of good quality and operating appropriately, and the other is that the testing environment is free from distractions.
Furthermore, a polygraph can only be performed when the person in question is in regular, stable mental and physical condition. In order to make sure that those tested remain in a stable state, the person administering the test should not only inform the accused of their right to refuse the procedure and about the effects a lie detector test may have, but the psychosomatic state of the subject should also be checked to verify that they are in a suitable psychological state.
All of these requirements clearly highlight how polygraph exams given under forced circumstances can not only damage the right to defense of the accused, but also how the results obtained from such a test may not adequately portray the truth.
Even though strict regulations on the use of lie detectors in the practice of criminal justice exist, it does not necessarily follow that these demands can be put into practice.
In spite of the polygrapher controlling the test environment and placing the person receiving the test in isolation, even if the subject was innocent, would they really be able to keep their mind and body in a normal state?